Combinatorial electrochemical deposition and testing system

ABSTRACT

An electrochemical deposition and testing system consisting of individually addressable electrode arrays, a fully automated deposition head, and a parallel screening apparatus is described. The system is capable of synthesizing and screening millions of new compositions at an unprecedented rate.

This application is a divisional of U.S. application Ser. No. 09/119,187filed on Jul. 20, 1998, now U.S. Pat. No. 6,187,164, which itself is acontinuation-in-part of U.S. application Ser. No. 08/941,170 filed Sep.30, 1997, now U.S. Pat. No. 6,468,806, the techniques of each of whichare incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for theelectrodeposition of diverse materials. More specifically, the inventioncomprises a fully automated electrochemical deposition and testingsystem for the synthesis and parallel screening of distinct materials onarrays of individually addressable electrodes.

BACKGROUND OF THE INVENTION

Among the different techniques for the preparation of metal deposits,electrodeposition (also known as electroplating) is particularlyattractive because of its relatively inexpensive instrumentation, lowtemperature operation, and simplicity. A further advantage of thetechnique is the relatively straightforward control of the thickness andcomposition of the depositing layers through electrical quantities suchas current passed and potential applied.

Electroplating has been employed in small scale as well as industrialprocesses. For example, electroplating of precious metals to improve theappearance of an article or to create special effects is well known.Electroplating is also employed to improve the corrosion resistance ofcorrosive substances by depositing thin surface films of corrosionresistant metals such as zinc, tin, chromium, nickel and others. Wearresistant and friction modifying coatings of nickel, chromium, titaniumand other metals and their alloys are used to improve the wearresistance of bearing surfaces. Electroplating is also employed in theelectronics industry to improve or modify the electrical properties ofsubstrates such as contacts, printed circuits, electrical conductors,and other electrical items in which specific surface orsurface-to-substrate conductive properties are desired. Distinct metalsare often electroplated onto metal surfaces to improve solderingcharacteristics or to facilitate subsequent coating by painting orapplication of other adhering films such as plastics, adhesives, rubber,or other materials.

Although the electrodeposition of a single material has been extensivelystudied, the deposition of two or more metals by electrochemical methodsis difficult because the conditions favorable for the deposition of onemetal may differ substantially with those necessary for the depositionof the other. Factors including widely differing reduction potentials,internal redox reactions that can alter the oxidation states of thematerials in solution, and species that are or become insoluble duringthe deposition can disrupt the process. Moreover, the nature of theelectrodeposit itself is determined by many factors including theelectrolyte composition, pH, temperature and agitation, the potentialapplied between the electrodes, and the current density. These issuesare more prevalent as the complexity of the electrodeposit (and hencethe number of species in solution) increases.

Complex electodeposited materials are desired in areas such as catalysiswhere the composition of the electrodeposit is critical to its catalyticactivity. The discovery of new catalytic materials depends largely onthe ability to synthesize and analyze new compounds. Given approximately100 elements in the periodic table that can be used to make suchcatalysts, and the fact that ternary, quaternary and greatercompositions are desired, an incredibly large number of possiblecompositions is generated. Taking each of the previously notedelectrochemical issues into account for every possible electrodepositand designing a synthetic strategy that can effectively cover phasespace using traditional synthetic methodologies is a time consuming andlaborious practice. As such, there exists a need in the art for a moreefficient, economical, and systematic approach for the synthesis ofnovel materials and for the screening of such materials for usefulproperties. See, for example, copending U.S. patent application Ser. No.08/327,513 entitled “The Combinatorial Synthesis of Novel Materials”(published as WO 96/11878).

As an example of the utility of exploring phase space for more effectivecatalysts, one can consider the effect of changing the composition ofthe anode in a direct methanol fuel cell. A tremendous amount ofresearch in this area has concentrated on exploring the activity ofsurface modified binary, and to a much lesser extent ternary, alloys ofplatinum in an attempt to both increase the efficiency of and reduce theamount of precious metals in the anode part of the fuel cell. Althoughelectrodeposition was explored as a route to the synthesis of anodematerials (e.g., F. Richarz et al. Surface Science, 1995, 335, 361),only a few compositions were actually prepared, and these compositionswere made using traditional single point electrodeposition techniques.Such an approach becomes very inefficient when exploring and optimizingnew multi-component systems. Recently, Mallouk, et al. reported work oncombinatorial electrochemistry as a route to fuel cell anode materials(Science, 1998, 280, 1735), but this technique did not employelectrodeposition techniques.

The present invention provides a method to use electrodeposition tosynthesize and evaluate large numbers of distinct materials inrelatively short periods of time, significantly reducing the timeconsuming and laborious processes normally associated with a novelmaterials discovery program.

SUMMARY OF THE INVENTION

This invention provides methods and apparatus for electrochemicallydepositing distinct materials on arrays of individually addressableelectrodes. The invention also provides a means of testing the asdeposited materials for specific properties of interest.

One embodiment of the invention includes the individually addressableelectrode arrays and their associated fabrication and processing steps.

Another embodiment of the invention includes an automated depositionsystem comprising a solution delivery head and its associatedelectronics and robotics. The delivery head is capable of automaticallydispensing precise mixtures of plating solutions to predefined locationsabove the working electrodes on the individually addressable electrodearrays. The head contains a reference and counter electrode, and whiledelivering the plating solutions completes a circuit with a givenworking electrode on the array. Adjusting the potential applied to theworking electrode on the array results in the deposition of materialsfrom the delivered plating solutions.

Another embodiment of the invention includes an electrochemical testingsystem comprising an electrochemical cell, a multi-channel potentiostat,and an electronic interface designed to couple the addressable array tothe potentiostat such that individual electrodes on the array may beaddressed, either serially or in parallel, for the measurement of aspecific material property under investigation.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the present invention, reference should bemade to the following detailed description taken in conjunction with theaccompanying drawings wherein:

FIG. 1A illustrates an array of 64 individually addressable electrodesmade in accordance with the present invention;

FIG. 1B illustrates an array of 66 individually addressable electrodesmade in accordance with the present invention;

FIG. 2A is a flow chart diagram describing the processes involved infabricating individually addressable electrode arrays;

FIGS. 2A and 2B are examples of masks for array fabrication;

FIG. 3 is a sectional view of the electrochemical deposition head;

FIG. 4A is a sectional view of the electrochemical cell;

FIG. 4B is a sectional view of the cathode assembly associated with theelectrochemical cell of FIG. 4A;

FIG. 4C is an exploded view of the anode assembly associated with theelectrochemical cell of FIG. 4A;

FIG. 4D is a sectional view of the PCB interface associated with theanode assembly of FIG. 4C;

FIG. 4E is a circuit diagram showing the electrical connections in thePCB interface of FIG. 4D; and

FIG. 5 is a graph illustrative of the relationship between electrodecomposition and associated activity for an example system synthesizedand measured using embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises an electrochemical synthesis and testingsystem consisting of a number of separate parts including individuallyaddressable electrode arrays, a fully automated deposition head, anelectrochemical cell and its associated electronics, and a multi-channelpotentiostat. These components provide a means for investigating complexmulti-component systems, by giving a user the ability to rapidlysynthesize and evaluate large numbers of diverse materials in shortperiods of time.

The individually addressable electrode arrays 10 of the presentinvention are illustrated in FIGS. 1A and 1B. The arrays 10 consist ofeither sixty-four or sixty-six independent electrodes 12 (with areas ofbetween 1 and 2 mm²) that are fabricated on inert substrates 14. Arrayswith as little as 10 or as many as 100 electrodes may be made inaccordance with the methods provided in the present invention. Examplesubstrates include, but are not limited to, glass, quartz, sapphire,alumina, plastics, or thermally treated silicon. Other suitablesubstrate materials will be readily apparent to those of skill in theart. The individual electrodes 12 are located substantially in thecenter of the substrate 14, and are connected to contact pads 13 aroundthe periphery of the substrate with wires 16. The electrodes 12,associated wires 16, and contact pads 13 are fabricated from conductingmaterials (such as gold, silver, platinum, copper, or other commonlyused electrode materials). In a preferred embodiment of the presentinvention, the arrays are fabricated on standard 3″ thermally oxidizedsingle crystal silicon wafers, and the electrodes are gold with surfaceareas of about 1.26 mm^(2.)

Still referring to FIGS. 1A and 1B, a patterned insulating layer 18covers the wires 16 and an inner portion of the peripheral contact pads13, but leaves the electrodes 12 and the outer portion of the peripheralcontact pads 13 exposed (preferably approximately half of the contactpad 13 is covered with this insulating layer). Because of the insulatinglayer 18, it is possible to connect a lead (e.g, an alligator clip) tothe outer portion of a given contact pad 13 and address its associatedelectrode 12 while the array 10 is immersed in solution, without havingto worry about reactions that can occur on the wires 16 or peripheralcontact pads. The insulting layer 18 may be, for example, glass, cilica(SiO₂), alumina (Al₂O₃), magnesium oxide (MgO), silicon nitride (Si₃N₄),boon nitride (BN), yttrium oxide (Y₂O₃), titanium dioxide (TiO₂),hardened photoresist, or other suitable material known to be insulatingin nature.

Once a suitable inert substrate is provided, photolithographictechniques can be applied to design and fabricate electrode arraypatterns on it. By applying a predetermined amount of photoresist to thesubstrate, photolyzing preselected regions of the photoresist, removingthose regions that have been photolyzed (e.g., by using an appropriatedeveloper), depositing one or more metals over the entire surface andremoving predetermined regions of these metals (e.g., by dissolving theunderlying photoresist), one can fabricate intricate patterns ofindividually addressable electrodes on the substrate.

The process by which the individually addressable electrode arrays ofthe present invention are fabricated is described with reference to theflow chart illustrated in FIG. 2A. Starting with a cleaning step 22 thatcomprises washing the wafer in a suitable solvent (such as methanol orisopropanol) followed by baking in a plasma cleaning oven, a photoresistdeposition step 24 in which a first layer of photoresist is applied tothe wafer is then done. Although many different types of photoresist canbe used for the same effect, the preferred type in the present inventionis Shipley Microposit S-1813 (or equivalent). The photoresist is appliedto the wafer using a standard spin coating system (commonly used andfamiliar to those skilled in the art) which is set to leave a finalthickness of between 1 and 2 μm on the wafer. The photoresist is thencured at a predetermined temperature for a predetermined time tocondition the photoresist. In a preferred embodiment of the presentinvention, the curing temperature is between 90° C. and 130° C. and thecuring time is between 30 sec and 2 minutes.

A primary electrode mask 27, an example of which is shown in FIG. 2B,(which is the negative of the electrode array pattern desired) is thenplaced over the wafer that is then photolyzed on a mask aligner system(commonly used and familiar to those skilled in the art). After exposureto ultraviolet (UV) light during the photolysis step 26, regions 29 onthe wafer are then dissolved away using an appropriate developingsolution (e.g., Shipley Microposit MF-319 or equivalent). The wafer isthen placed in a physical vapor deposition (PVD) system where a metalsare deposited during a metal deposition step 28. Example PVD systemsinclude: sputtering, electron beam evaporation and pulsed laserdeposition. The metals deposited by the appropriate PVD system consistof an adhesion layer (such as Cr, Ta, or W) followed by the desiredelectrode material (such as Au, Ag Cu or Pt). The thicknesses of theselayers may vary substantially, but are typically 100-500 Å for theadhesion layer and 1000-5000 Å for the electrode layer. Following alift-off step 30 to remove the excess metals, a second layer ofphotoresist is then deposited on the wafer during a second photoresistdeposition step 32, cured as described above, and photolyzed through anisolation mask 35 during a second photolysis step 34. The aim of thissecond photolysis step is to expose only the regions of the electrodepads 36 and an outer contact ring 38, the exposed photoresist on whichis dissolved away after the photolysis step. A final annealing step 40at between 90° C. and 130° C. for between 1 minute and 10 (or more)minutes hardens the remaining photoresist into an effective insulatinglayer. Alternately, an insulating layer (such as glass, silica, alumina,magnesium oxide, silicon nitride, boron nitride, yttrium oxide ortitanium dioxide) may be deposited in place of the hardened photoresistby a suitable PVD technique after photolysis of the second photoresistlayer through an inverse isolation mask (the negative of the isolationmask 35 in FIG. 2C).

The arrays of the present invention consist of a plurality ofindividually addressable electrodes that are insulated from each other(by adequate spacing) and from the substrate (since they are fabricatedon an insulating substrate), and whose interconnects are insulated fromthe electrochemical testing solution (by the hardened photoresist orother suitable insulating material). The number of electrodes can varyaccording to a desired number, but typically the arrays consist of 10 ormore electrodes, 30 or more electrodes, and preferably more than 50electrodes. In the embodiments shown in FIG. 1A and FIG. 1B, more than60 electrodes are in a single array. Materials are deposited on each ofthe individually addressable electrodes. Thus, an array of individuallyaddressable materials is also a part of this invention, with the numberof materials equaling the number of addressable electrodes. Thematerials in the array may be the same or different, as described below.

The deposition of materials on the above described electrode arrays tomake a library of an equal number of compositions is accomplished by theelectrodeposition of species from solution using standardelectrochemical methods. The compositions may all be the same, or may bedifferent from each other. In one embodiment of the present invention,the depositions are carried out by immersing the electrode array in astandard electrochemical deposition chamber containing the array, aplatinum mesh counter electrode, and a reference electrode (e.g.,Ag/AgCl). The chamber is filled with a plating solution containing knownamounts of source materials to be deposited. By selecting a givenelectrode and applying a predetermined potential for a predeterminedamount of time, a particular composition of materials (which may or maynot correspond to the exact composition of the plating solution) isdeposited on the electrode surface. Variations in the compositionsdeposited may be obtained either by directly changing the solutioncomposition for each deposition or by using different electrochemicaldeposition techniques, or both. Examples of how one may change theelectrode composition by changing the deposition technique can include:changing the deposition potential, changing the length of the depositiontime, varying the counter anions, using different concentrations of eachspecies, and even using different electrochemical deposition programs(e.g., potentiostatic oxidation/reduction, galvanostaticoxidation/reduction, potential square-wave voltammetry, potentialstair-step voltammetry, etc.). Through repeated deposition steps, avariety of materials may be serially deposited on the array for theaforementioned library.

In an alternate embodiment of the present invention, the deposition ofmaterials on the electrode array is carried out using a partially orfully automated solution delivery/electroplating system consisting of adeposition head and its associated syringe pumps, robotics andelectronics. As illustrated in FIG. 3, the deposition head 50 consistsof a rod 52 that is tapered at the tip. The tapered end of thedeposition head is wrapped with a mesh counter electrode 54 (e.g., Pt)that is connected to an external power supply (not shown) via a wire 56that is embedded in the wall of the head. In a preferred embodiment ofthe present invention, the deposition head has a 1-3 mm ID which istapered to ca. 1 mm ID at the tip. A solution delivery tube 58containing an interannular reference electrode 60 is located into thecenter of the rod 52. The reference electrode 60 may be a standardreference electrode (such as Ag/AgCl, SHE, SCE or Hg/HgSO₄) or aquasi-reference electrode (such as a piece of Pt wire). The referenceelectrode 60 is split off from the solution delivery tube 58 andconnected to an external power supply or potentiostat (not shown). Theflow of liquids through the solution delivery tube 58 is controlled bycommercially available syringe pumps (not shown) that can preciselydeliver volumes of liquids with accurate displacements in the μL/hourregime. Although any number of syringe pumps can be used, at least oneis desirable and the exact number of pumps will ultimately depend on thecomplexity of the desired depositions (i.e., binary=two pumps,ternary=three pumps, quaternary=four pumps, etc.). The liquids that aredispensed from the aforementioned pumps are either mixed prior toentering the solution delivery tube (via an external mixer) or via afrit 62 embedded in the deposition head. During the deposition process,the deposition head 50 is held over a given electrode pad 12 on anelectrode array 10 by a clamp 68 that is connected to robotics (notshown) that can control its precise position. In a preferred embodimentof the present invention, the ideal position, as illustrated in FIG. 3,is ca. 1-2 mm above the electrode pad 12.

Still referring to FIG. 3, the operation of the automated depositionsystem is described as follows. After positioning the deposition headabove a given electrode (sometimes referred to as the ‘working’electrode), the syringe pumps are activated causing a predeterminedmixture of liquids containing predetermined amounts of source materialsto flow through the tube 58 at an exactly specified flow rate andcollect in a region 70 surrounding a given electrode 12. When the liquidcontacts all three electrodes, a complete electric circuit is formed inthis region. Coincident with the formation of this circuit, apredetermined potential is applied to the working electrode (via anexternal power supply or potentiostat) causing species present in theliquid above it to deposit on the electrode surface. After apredetermined deposition time, the head is rinsed and moved to the nextelectrode where the next specified mixture is delivered and plated out.In a preferred embodiment of the present invention, a deposition time ofbetween 1 and 2 minutes is used. The entire procedure can take less than3 minutes per deposition or about three hours per library of sixty-fourto sixty-six elements.

The electrochemical cell used to measure properties of the materialsdeposited on the above described electrode arrays is illustrated inFIGS. 4A-4E. Referring to FIGS. 4A-4B, the cell 80 comprises acylindrical glass housing 82 (of approximate diameter equal to that ofthe wafers) that is sandwiched between two plastic end members 84. Theanode array assembly 86, which holds the individually addressableelectrode arrays 10, is fit into one side of the cell, and the cathodeassembly 95, which holds a counter electrode 88 and its associatedexternal wire coupling 96, is fit into the other side. The cell is heldtogether by four screw fasteners 90 which fit through holes 98 locatedon the corners of the end members 84. A reference electrode compartment92 is bored into the glass housing to allow the insertion of a referenceelectrode (not shown). A liquid filling hole 94 allows for the fillingand drainage of testing solutions from the electrochemical cell.

Referring to FIG. 4C, an exploded view of the components of the anodeassembly is shown. The glass housing 82 of the cell is fit over theinner flange 106 of a molded adapter 102 and is held in place againstthe adapter with an o-ring 100. This o-ring provides a water-tight sealfor this part of the assembly. The diameter of the outer flange 104 ofthe adapter 102 is the same as that of the glass housing, while that ofthe inner flange 106 is slightly smaller allowing one half of it to fitinto the glass housing and the other half of it to fit into theremaining pieces of the anode assembly. A groove 108 is cut into thelower lip of the adapter 102. This groove holds an o-ring 110 whichmakes a water-tight seal with the anode array 10 when the adapter ispressed against it. Electrical contact to the anode array 10 is madeusing a ring of elastomeric contacts 114 which are pressed between theperipheral pads of the array (see FIGS. 1A-1B) and contact pads 122 on aprinted circuit board (PCB) assembly 112. These elastomeric contactscontain miniature wires encased in a flexible rubber sheath. They arecommercially available and known to those skilled in the art. The anodearray 10 is affixed to a backing plate 116 and attached to the PCB 112with screws (not shown) through holes 118. This backing plate holds theelectrode array and ensures contact between the peripheral pads on thewafer and the contacts on the PCB. This completes the anode assemblywhich is fitted together with screw fasteners 90 through holes 98 in endmember 84 as shown in FIG. 4A.

Referring now to FIGS. 4D-4E, the PCB 112 and its associated circuitdiagram 130 are described as follows. The PCB 112 consists of arectangular plate 120 on which is deposited an intricate pattern ofwires and connectors. The contact pads 122, which provide electricalconnection to peripheral pads on the anode array (FIGS. 1A-1B), arerouted to four high-density pin connectors 128 that provide a cableconnection to an external power supply (not shown) or multi-channelpotentiostat 132. The multi-channel potentiostat 132 is essentially acollection of individual potentiostats bundled together in a singleunit. These individual potentiostats can precisely control the currentor potential applied to each electrode in the system. A common referenceelectrode contact 124 and a common counter electrode contact 126 arealso wired to the high density pin connectors so that individualelectrode pads on a given electrode array may be connected to the samereference and counter electrode during test measurements in theelectrochemical cell.

Using the PCB 112 in conjunction with the deposition head 50 (FIG. 3)and the multi-channel potentiostat, each individual electrode on a givenanode array can be individually addressed (e.g., during aelectrodeposition procedure). Alternatively, using the PCB in connectionwith the electrochemical cell whip 80 (FIG. 4A) and multi-channelpotentiostat, all of the electrodes on the array may be simultaneouslyaddressed (e.g., during a catalytic activity measurement). Suchcatalytic measurements can be made in a time fame of between 1 and 2minutes for each array of materials.

In the PCB illustrated in FIG. 4D, a sixty-four contact padconfiguration is shown. It should be understood that a sixty-six contactpad configuration would be needed for experiments using a sixty-sixmember electrode array (FIG. 1B), and that PCB's having greater or lesscontact pads and associated connections are straightforward extensionsof the concept and intended to be included within the scope of thepresent invention.

EXAMPLE

The following example illustrates the electrochemical deposition andscreening measurements for a very specific system using selectedembodiments of the present invention. It is only one of the manypossible uses of the present invention. The example illustrates how alibrary of sixty-four different Pt—Ru compositions may be prepared andtested for methanol oxidation activity. It should be understood that thesolution and electrode compositions, types of reference and counterelectrodes, applied and measured potentials, screening test conditions,and associated results are merely illustrative and that a person skilledin the art may make reasonable substitutions or modifications to thesecomponents without deviating from the spirit and scope of the invention.

A binary Pt—Ru library containing sixty-four different Pt—Rucompositions was synthesized on a sixty-four element individuallyaddressable electrode array (gold electrodes) using the electrochemicalreduction of acidic solutions containing mixtures of platinum chloride(H₂PtCl₆) and ruthenium chloride (RuCl₃). Starting with a stock solutionof 150 ml of 0.01M RuCl₃ (in 0.5M H₂SO₄) that was placed in a standardelectrochemical deposition chamber along with the electrode array, a Ptmesh counter electrode, and a silver/silver chloride (Ag/AgCl) referenceelectrode, the first working electrode on the array was held at aconstant potential of −0.25V (vs Ag/AgCl) for two minutes under constantstirring. The electrode array was then rotated in the deposition chamberand the solution composition adjusted (by the removal of a 5 ml aliquotof the RuCl₃ solution and its replacement with a 5 ml aliquot of a 0.01MH₂PtCl₆ solution), where the next electrode was deposited at the samepotential and for the same amount of time. This procedure was continueduntil all sixty-four electrodes were deposited with Pt—Ru compositions,whose thickness averaged between 1000-2000. Analysis (via X-rayfluorescence measurements) of the sixty-four electrodes showed acontinuously varying gradient of Ru and Pt compositions among thesixty-four electrodes on the array.

This Pt—Ru library was then screened for methanol oxidation activity byplacing it into the electrochemical cell (described earlier) which wasfilled with a solution of 1.0M methanol in 0.5M H₂SO₄ (a standardtesting solution composition for studying the electrooxidation ofmethanol in fuel cells). The cell also contained a Hg/HgSO₄ referenceelectrode and a Pt mesh counter electrode. Chronoamperometrymeasurements (i.e., holding a given electrode at a given potential andmeasuring the current that passes as a function of time) were thenperformed on all of the electrodes in the library by pulsing eachindividual electrode to a potential of −0.125V (vs Hg/HgSO₄) and holdingit there for 1 minute while monitoring and recording the current thatpassed. The results of this experiment are depicted in FIG. 5.

Referring now to FIG. 5, a three-dimensional plot 140 of electrodecomposition 142 (expressed as mole fraction platinum) versus current 144(in amps per square centimeter) versus time 146 (in seconds) isdisplayed. Individual electrodes are represented by their compositionsalong the x-axis, with their associated activities represented by theircurrent values on the z-axis. The most active electrode compositions 150are centered around a 50:50 Pt:Ru electrode composition which agreeswith results reported in the literature (e.g., D. Chu and S. Gilman, J.Electrochem. Soc. 1996, 143, 1685). Although the results plotted in FIG.5 correspond to a simple binary library of Pt—Ru compositions made bythe serial deposition of Pt—Ru solutions in a standard depositionchamber and studied by serial chronoamperometry measurements made on asingle channel potentiostat, the same depositions and measurements couldbe made in parallel with a multi-potentiostat using the deposition headand PCB interface of the present invention (FIGS. 3 and 4D). In fact,significantly more complicated libraries using ternary, quaternary andgreater compositions are possibly simply by changing the composition ofthe initial plating solutions. Plating solutions comprising one or moreof the water soluble forms of the transition elements (e.g., Sc, Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta,W. Re, Os, Ir, Pt, Au, Hg) as well as many main group elements (e.g.,Al, Ga, Ge, In, Sn, Sb, Te, Tl, Pb, Bi) can be used with the presentinvention, and will give rise to enormous variations in librarycompositions which can in turn be studied in an enormous variety ofcatalytic systems.

As should now be readily apparent, the present invention provides a farsuperior method of electrochemically depositing and screening theproperties of diverse materials. Using this invention, one canefficiently prepare libraries of varying elemental composition, and,since these libraries are prepared on individually addressable electrodearrays, one can also directly measure properties of these compositions.Using the present invention, it should be possible to synthesize andscreen millions of new compositions at an unprecedented rate.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reading the above description. The scopeof the invention should, therefore, be determined not with reference tothe above description, but should instead be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. The disclosures of all articles andreferences, including patent applications and publications, areincorporated herein by reference for all purposes.

What is claimed is:
 1. A system for electrochemically screening an arrayof materials, said system comprising: (a) an array of differentmaterials having an individually addressable electrode corresponding toeach different material in the array; and (b) means associated with eachof said electrodes for simultaneously testing each of said materials fora common selected property, said means comprising an electrochemicalcell, a multi-channel potentiostat, and a printed circuit boardassembly, wherein said electrochemical cell comprises: a cylindricalglass housing, said housing sandwiched between end members and held inplace with fasteners; a reference electrode compartment; a liquidfilling hole; a cathode assembly; and an anode array assembly, saidanode array assembly holding said array of individually addressableelectrodes.
 2. The system of claim 1, wherein said anode array assemblycomprises: a first o-ring, said first o-ring forming a water-tight sealwith said glass housing; a molded adapter having an inner flange, anouter flange, and at least one groove; an array of individuallyaddressable electrodes; a second o-ring, said second o-ring fitting intosaid groove and forming a water-tight seal with said array ofindividually addressable electrodes; a printed circuit board; a ring ofelastomeric contacts, said elastomeric contacts located between saidarray and said printed circuit board; and a backing plate.
 3. The systemof claim 2, wherein said printed circuit board comprises: apredetermined number of contact pads, said number of contact padscorresponding to the number of individually addressable electrodes onsaid array; at least four high density pin connectors; a commonreference electrode contact; and a common counter electrode contact. 4.A system for electrochemically screening an array of materials, thesystem comprising an electrochemical cell comprising (i) an electrodearray assembly comprising an array of two or more individuallyaddressable electrodes, each of the two or more electrodes being adaptedfor supporting a member of the array of materials, the array of two ormore individually addressable electrodes being on a substrate thatfurther comprises two or more contact pads on the substrate, each of thetwo or more contact pads being electrically connected to a correspondingone of the two or more electrodes, the electrode array assembly furthercomprising a printed circuit board assembly comprising two or morecontact pads arranged to correspond to the arrangement of contact padson the substrate, the printed circuit board assembly providingelectrical communication between the multi-channel potentiostat and eachof the two or more electrodes of the array through the contact pads ofthe printed circuit board assembly and the corresponding contact pads onthe substrate, (ii) a counter electrode, and (iii) a housing, configuredin combination to define a cell for containing a liquid test solutionsuch that each of the two or more electrodes or members supportedthereon contact the test solution, and a multichannel potentiostat inelectrical communication with the array of addressable electrodes forcontrolling the current or potential applied to each of the two or moreelectrodes of the array.
 5. The system of claim 4 further comprising areference electrode disposed within the housing and in electricalcommunication with the multi-channel potentiostat.
 6. The system ofclaim 4 wherein the housing is sealingly engaged with the electrodearray assembly.
 7. The system of claim 4 wherein the substrate comprisesthe two or more contact pads disposed around a periphery of thesubstrate.
 8. The system of claim 4 wherein the electrode array assemblyfurther comprises an elastomeric contact pressed between the contactspads of the printed circuit board assembly and the corresponding contactpads on the substrate, the elastomeric contact comprising wiresproviding electrical communication between the contact pads of theprinted circuit board assembly and the corresponding contact pads on thesubstrate.
 9. The system of claim 4 wherein the electrochemical cellfurther comprises an aperture for filling the electrochemical cell witha test solution or for draining a test solution from the electrochemicalcell.